Editors’ note: For the April edition of Expert Perspectives, we asked 2 leading neurologists to present differing views on the use of calcitonin gene-related peptide (CGRP) monoclonal antibodies (mAbs) for the treatment of migraine. Here, Lawrence Robbins, MD, of the Robbins Headache Clinic in Riverwoods, IL, discusses potential safety concerns associated with this drug class. To read a counterargument in which Jack D. Schim, MD, of the Neurology Center of Southern California, discusses the observed benefits of CGRP mAbs, click here .
Lawrence Robbins, MD is an associate professor of neurology at Chicago Medical School and is in private practice in Riverwoods, IL.
Dr. Robbins discloses speaker’s bureau remuneration from AbbVie, Amgen, Biohaven, Impel NeuroPharma, Lundbeck, and Teva.
The calcitonin gene-related peptide (CGRP) monoclonal antibodies (mAbs) were introduced in 2018 as efficacious with few adverse effects. Unfortunately, the phase 3 trials failed to indicate the considerable number of adverse effects that have since been identified. This is a common occurrence with new drugs and mAbs.
There are few adverse events identified in the package insert (PI) for any of the 4 CGRP mAbs, but again that is not restricted to this class. Post-approval, it frequently takes time to piece together the true adverse effect profile. Reasons that phase 3 studies may miss adverse effects include 1) The studies are powered for efficacy but are not powered for adverse effects in terms of both the number of patients and the length of the study; 2) Studies do not use a checklist of likely adverse effects; and 3) Adverse effects become “disaggregated” (for example, 1 person states they have malaise, another tiredness, and another fatigue).
In the ensuing years since the launch of the CGRP mAbs, various lines of evidence pointed to the adverse effects attributed to these mAbs. These include the US Food and Drug Administration (FDA)/FDA Adverse Event Reporting System (FAERS) website, published studies, the collective experience of high prescribers, and filtered comments from patient chat boards. In addition, I have received hundreds of letters from providers and patients regarding serious adverse effects, which are detailed further in this article.
As of March 2022, the FDA/FAERS website has listed approximately 50,000 adverse events in connection with the CGRP mAbs. The number of serious events (hospitalization or life-threatening issues) was about 7000. These large numbers, just 3.75 years after launch, are like those listed for onabotulinumtoxin A after 30 years! Most of the reports involve erenumab. This is because erenumab was approved first and is the most prescribed drug in this class. I do not believe it is more dangerous than the others. Considering that the vast majority of adverse events go unreported, these are staggering numbers. Regarding serious adverse events, only 1% to 10% are actually reported to the FDA. Nobody knows the true percentage of milder adverse events that are actually reported, but in my experience, it is extremely low.
Unfortunately, the FDA/FAERS website lists on only adverse events, not adverse effects, which are just as important to discuss. In my small practice I have observed 4 serious adverse effects in women I believe are attributable to CGRP mAbs. These include a cerebrovascular accident in a 21-year-old patient, a case of reversible cerebral vasoconstrictive syndrome in a 61-year-old patient, severe joint pain in a 66-year-old patient, and a constellation of symptoms that resembled multiple sclerosis in a 30-year-old patient. I have administered onabotulinumtoxinA to thousands of patients for 25 years, with no serious adverse effects.
There have been a number of post-approval articles, studies, and case reports published since the launch of the CGRP mAbs. Many “review” or “meta-analysis” articles tend to repeat the results of the pharma-sponsored studies. They typically characterize the CGRP mAbs as safe, with few adverse events. Long-term safety extension studies almost always conclude that the drug is safe. In my opinion, the results from these studies are not reliable because of their possible ties to phrama.
Other studies tell a different tale. One observational study of erenumab concluded that adverse effects contributed to 33% of the discontinuations. Another study reported that 63.3% of patients taking mAbs described at least 1 adverse effect . A study of patients who had been prescribed erenumab indicated that 48% reported a non-serious adverse event after 3 months.
Neurologists are generally unaware of the dangers posed by CGRP mAbs. In September 2021, I engaged in a debate on this topic during the International 15th World Congress on Controversies in Neurology (CONy). Prior to the debate, the audience members were polled. 94% believed the CGRP mAbs to be safe. After our debate, only 40% felt that these mAbs were safe. I think that the audience, primarily consisting of neurologists, was not informed as to the potential dangers of the CGRP mAbs.
In our practice
For refractory patients, I do prescribe these CGRP mAbs. However, I feel they should only be prescribed after several other, safer options have failed. These include the natural approaches (butterbur, magnesium, riboflavin), several of the standard medications (amitriptyline, beta blockers, topiramate, valproate, angiotensin II receptor blockers), and onabotulinumtoxinA. Additionally, the newer gepants for prevention (rimegepant and atogepant) appear to be safer options than the CGRP mAbs, although we cannot say this definitively at this time.
In 2018, our clinic began a retrospective study that lasted until January 2020. We assessed 119 patients with chronic migraine who had been prescribed one of the CGRP mAbs. This study incorporated the use of a checklist of possible adverse effects. Each of these adverse effects had created a “signal.” We initially asked the patients, “Have you experienced any issues, problems, or side effects due to the CGRP monoclonal antibody?” The patients subsequently were interviewed and asked about each possible adverse effect included on the checklist. The patient and physician determined whether any adverse effect mentioned by the patient was due to the CGRP mAb. After discussing the checklist, 66% of the patients concluded they had experienced 1 additional adverse effect that they attributed to the CGRP mAb and had not originally disclosed in response to the initial question. Most of these patients identified more than 1 additional adverse effect through use of the checklist.
Gathering data
To determine the true adverse event profile post-approval, we rely upon the input of high prescribers, who often can provide this necessary feedback. I have assessed input from headache provider chat boards, private correspondence with many providers, and discussions with colleagues at conferences. The opinions do vary, with some headache providers arguing that there are not that many adverse effects arising from the CGRP mAbs. Many others believe, as I do, that there are a large number of adverse events. In my observations, there is not a consensus among headache providers.
The CGRP patient chat boards are another valuable line of evidence. I have screened 2800 comments from patients regarding adverse events. I filtered these down into 490 “highly believable” comments. Among those, the adverse events described align very well with our other lines of evidence.
If we put all the post-approval lines of evidence together, we come up with the following list of “adverse effect signals” attribututed to the CGRP mAbs. These include constipation (it may be severe; hence the warning in the erenumab PI), injection site reactions, joint pain, anxiety, muscle pain or cramps, hypertension or worsening hypertension (there is a warning in the erenumab PI), nausea (it may be severe; “area postrema syndrome” has occurred), rash, increased headache, fatigue, depression, insomnia, hair loss, tachycardia (and other cardiac arrhythmias), stroke, angina and myocardial infarction, weight gain or loss, irritability, and sexual dysfunction. There are also other adverse events. In his review of the CGRP mAbs, Thomas Moore, a leading expert in adverse events, cited the “sheer number of case reports, and it is likely that AEs of this migraine preventive were underestimated in the clinical trials.”
This discussion has focused on short-term adverse events. We have no idea regarding long-term effects, but I suspect that we will encounter serious ones. Evolution has deemed CGRP to be vital for 450 million years. We ignore evolution at our peril.
CGRP is a powerful vasodilator and protects our cardiovascular and cerebrovascular systems. CGRP resists the onset of hypertension. Wound and burn healing, as well as tissue repair, require CGRP. Bony metabolism and bone healing are partly dependent upon CGRP. CGRP protects from gastrointestinal (GI) ulcers and aids GI motility. CGRP mitigates the effects of sepsis.
CGRP is also involved with flushing, thermoregulation, cold hypersensitivity, protecting the kidneys when under stress, helping regulate insulin release, and mediating the adrenal glucocorticoid response to acute stress (particularly in the mature fetus). Effects on the hypothalamic-pituitary-adrenal axis are worrisome but unknown. CGRP is important as a vasodilator during stress, and the CGRP mAbs have not yet been tested under stress.
The CGRP mAbs have been terrific for many patients, and their efficacy is on par with onabotulinumtoxinA. However, in a short period of time we have witnessed a plethora of serious (and non-serious) adverse effects from short-term use. CGRP plays an important role in many physiologic processes. We have no idea as to the long-term consequences of blocking CGRP and we should proceed with caution.